In addition to obtaining data for Childhood Leukemia and Residential and Electromagnetic Fields, the contractor shall also purchase, place, collect, and arrange for reading of detectors in the current and former residences of 600 ALL cases and 600 controls in this collaborative study. A trained technician will visit each home and obtain information about structural and other characteristics of the residence that pertains to radon exposure. One detector will be placed in 2-3 rooms (child's bedroom, family/living room, and bedroom where the mother was pregnant with the child, if applicable), with placement and associated quality control efforts performed in accordance in EPA's Indoor Radon and Radon Decay Product Measurement Protocols. The detectors will remain in the residence for a full year to eliminate seasonal variation in radon concentrations. The current residents will be contacted every 3-6 months to confirm that the detectors are in place and to determine whether current occupants plan to move shortly from the residence. After one year, the current residents will be contacted by phone and given instructions on how to return the detectors to the contractor for shipment to the processing facility. To facilitate and keep track of all information, the contractors will set up a data management system. Radon exposure data will be analyzed jointly by NCI, EPA, and Childrens' Cancer Study Group investigators. Radon exposure results for individual residences will be sent to participants by the contractor together with an interpretation of these results and any appropriate EPA recommendations.